Parent Company Only Financial Information (Details) - USD ($)	3 Months Ended												12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment in unconsolidated subsidiaries:
Other assets																$ 1,520,757,000	$ 1,220,435,000
Total assets																34,932,860,000	27,805,496,000
Liabilities and Equity [Abstract]
Subordinated debt and other borrowings																670,575,000	749,080,000
Other Liabilities																411,074,000	288,569,000
Stockholders' equity																4,904,611,000	4,355,748,000	$ 3,965,940,000	$ 3,707,952,000
Total liabilities and stockholders' equity																34,932,860,000	27,805,496,000
Expenses:
Interest expense - subordinated debentures													$ 199,254,000	$ 301,794,000	$ 210,375,000
Personnel expense, including stock compensation													334,483,000	313,359,000	271,673,000
Income tax expense (benefit)													59,037,000	96,656,000	90,508,000
Net income	$ 110,876,000	$ 110,645,000	$ 62,444,000	$ 28,356,000									312,321,000	400,881,000	359,440,000
Preferred stock dividends													7,596,000	0	0
Net income available to common shareholders	107,078,000	106,847,000	62,444,000	28,356,000	$ 96,079,000	$ 110,521,000	$ 100,321,000	$ 93,960,000	$ 95,318,000	$ 93,747,000	$ 86,865,000	$ 83,510,000	304,725,000	400,881,000	359,440,000
CONDENSED STATEMENTS OF CASH FLOWS [Abstract]
Net income	110,876,000	$ 110,645,000	$ 62,444,000	28,356,000									312,321,000	400,881,000	359,440,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization and accretion													45,203,000	8,342,000	(23,604,000)
Stock-based compensation expense													18,737,000	21,226,000	17,636,000
Deferred tax (expense) benefit													(58,315,000)	14,696,000	11,765,000
Income from equity method investment													(83,539,000)	(90,111,000)	(51,222,000)
Dividends received from equity method investment													53,020,000	51,312,000	33,651,000
Excess tax benefit from stock compensation													(417,000)	(1,011,000)	(2,966,000)
(Increase) decrease in other assets													(157,294,000)	(57,499,000)	(24,471,000)
Increase in other liabilities													81,322,000	79,264,000	60,617,000
Net cash provided by operating activities													427,825,000	434,288,000	470,757,000
Investing activities:
Increase in other investments													(71,254,000)	(55,926,000)	(56,918,000)
Net cash used in investing activities													(3,568,662,000)	(2,619,061,000)	(2,969,084,000)
Financing activities:
Repayments of other borrowings													136,661,000	184,175,000	620,000
Issuance of common stock pursuant to restricted stock unit agreement, net of shares withheld for taxes													(2,488,000)	0	0
Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants													217,126,000	0	0
Repurchase of common stock													(50,790,000)	(61,416,000)	(20,694,000)
Common dividends paid													49,389,000	49,828,000	45,454,000
Preferred stock dividends paid													7,596,000	0	0
Net cash provided by financing activities													6,575,579,000	1,989,788,000	2,440,423,000
Investment Income, Dividend													119,100,000	114,000,000.0	83,100,000
Parent Company
Assets [Abstract]
Cash and cash equivalents	275,888,000			182,091,000	182,091,000			94,043,000	94,043,000			64,851,000	182,091,000	94,043,000	64,851,000	275,888,000	182,091,000	$ 94,043,000	$ 64,851,000
Investment in unconsolidated subsidiaries:
Unconsolidated subsidiaries																3,995,000	3,995,000
Other investments																113,445,000	97,459,000
Current income tax receivable																51,621,000	11,696,000
Other assets																25,747,000	29,566,000
Total assets																5,452,178,000	4,985,933,000
Liabilities and Equity [Abstract]
Taxes Payable																0	2,467,000
Subordinated debt and other borrowings																541,286,000	620,256,000
Other Liabilities																6,281,000	7,462,000
Stockholders' equity																4,904,611,000	4,355,748,000
Total liabilities and stockholders' equity																5,452,178,000	4,985,933,000
CONDENSED STATEMENTS OF OPERATIONS [Abstract]
Income from equity method investment													22,587,000	24,298,000	13,731,000
Other income (loss)													3,861,000	3,485,000	1,310,000
Expenses:
Interest expense - subordinated debentures													23,877,000	18,425,000	17,703,000
Personnel expense, including stock compensation													18,737,000	21,226,000	17,636,000
Other expense													2,905,000	1,496,000	1,312,000
Income before income taxes and equity in undistributed income of subsidiaries													100,113,000	100,796,000	61,650,000
Income tax expense (benefit)													(5,370,000)	(4,457,000)	(8,570,000)
Income before equity in undistributed income of subsidiaries													105,483,000	105,253,000	70,220,000
Equity in undistributed income of bank subsidiaries													205,327,000	294,354,000	288,728,000
Equity in undistributed income (loss) of nonbank subsidiaries													1,511,000	1,274,000	492,000
Net income													312,321,000	400,881,000	359,440,000
Preferred stock dividends													7,596,000	0	0
Net income available to common shareholders													304,725,000	400,881,000	359,440,000
CONDENSED STATEMENTS OF CASH FLOWS [Abstract]
Net income													312,321,000	400,881,000	359,440,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization and accretion													1,122,000	(3,094,000)	105,000
Stock-based compensation expense													18,737,000	21,226,000	17,636,000
Increase (Decrease) in Income Taxes Payable, Net of Income Taxes Receivable													(2,467,000)	2,467,000	(24,000)
Deferred tax (expense) benefit													3,876,000	(2,857,000)	(549,000)
Income from equity method investment													(22,587,000)	(24,298,000)	(13,731,000)
Dividends received from equity method investment													9,251,000	8,953,000	5,872,000
Excess tax benefit from stock compensation													(417,000)	(1,011,000)	(2,966,000)
Gain on other investments													(195,000)	(1,057,000)	(209,000)
(Increase) decrease in other assets													(39,981,000)	7,295,000	4,390,000
Increase in other liabilities													(764,000)	5,322,000	2,758,000
Equity in undistributed (income) loss of bank subsidiaries													(205,327,000)	(294,354,000)	(288,728,000)
Equity in undistributed (income) loss of nonbank subsidiaries													(1,511,000)	(1,274,000)	(492,000)
Net cash provided by operating activities													72,058,000	118,199,000	83,502,000
Investing activities:
Investment in consolidated banking subsidiaries													0	(180,000,000)	0
Increase in other investments													(2,454,000)	(1,411,000)	(2,321,000)
Net cash used in investing activities													(2,454,000)	(181,411,000)	(2,321,000)
Proceeds from (Repayments of) Debt													(93,000)	316,078,000	19,850,000
Financing activities:
Repayments of other borrowings													80,000,000	49,880,000	620,000
Issuance of common stock pursuant to restricted stock unit agreement, net of shares withheld for taxes													(2,488,000)	0	0
Exercise of common stock options, net of shares surrendered for taxes													(2,577,000)	(3,694,000)	(5,071,000)
Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants													217,126,000	0	0
Repurchase of common stock													(50,790,000)	(61,416,000)	(20,694,000)
Common dividends paid													(49,389,000)	(49,828,000)	(45,454,000)
Preferred stock dividends paid													(7,596,000)	0	0
Net cash provided by financing activities													24,193,000	151,260,000	(51,989,000)
Cash and Cash Equivalents, Period Increase (Decrease)													93,797,000	88,048,000	29,192,000
Cash and cash equivalents, beginning of year				$ 182,091,000				$ 94,043,000				$ 64,851,000	182,091,000	94,043,000	64,851,000
Cash and cash equivalents, end of year	$ 275,888,000				$ 182,091,000				$ 94,043,000				275,888,000	182,091,000	94,043,000
Banking
Assets [Abstract]
Investments in consolidated subsidiaries																4,972,160,000	4,653,310,000
CONDENSED STATEMENTS OF OPERATIONS [Abstract]
Income from bank subsidiaries													119,065,000	113,982,000	83,090,000
Nonbank subsidiaries
Assets [Abstract]
Investments in consolidated subsidiaries																$ 9,322,000	$ 7,816,000
CONDENSED STATEMENTS OF OPERATIONS [Abstract]
Income from bank subsidiaries													$ 119,000	$ 178,000	$ 170,000